As for the prior art arrangement for controlling a bulldozer blade, there is, for example, one disclosed in U.S. Pat. No. 4,081,036. According to this prior art example, a bulldozer blade is connected to a U-shaped frame through a universal joint means in such a manner that it may be moved up and down, angled to the left and right, and tilted to the left and right relative to the U-shaped frame.
Briefly, by extending or retracting rods of a pair of lifting hydraulic cylinders in the same direction relative to each other, the U-shaped frame is turned vertically about a pair of left and right trunnion shafts for mounting the U-shaped frame onto the vehicle body, so that the blade is moved up and down while it is maintaining its horizontal position.
Further, when rods of a pair of left and right angling hydraulic cylinders are extended or retracted in opposite directions relative to each other, the blade is angled through the universal joint means to the left or to the right.
Further, when the rod of a tilting hydraulic cylinder mounted on the front end of the U-shaped frame substantially in parallel relationship with the blade is extended or retracted, the blade is tilted through a supporting means to the left or to the right.
Thus, the prior art arrangement for controlling a bulldozer blade comprises five hydraulic cylinders for controlling the operation of the blade. The arrangement is made such that by actuating the rods of the five hydraulic cylinders the blade can perform six operations, in total, i.e. upward and downward movements, angling to the left and right, and tilting to the left and right.
However, even by actuating the five hydraulic cylinders, the blade cannot be inclined forwardly or rearwardly as desired; that is, pitching operation of the blade cannot be conducted.